The use of microelectronic devices, such as integrated circuits, flat panel displays and microelectromechanical systems, has burgeoned in new business and consumer electronic equipment, such as personal computers, cellular phones, electronic calendars, personal digital assistants, and medical electronics. Such devices have also become an integral part of more established consumer products such as televisions, stereo components and automobiles.
These devices in turn contain one or more very high quality semiconductor chips containing many layers of circuit patterns. Typically nearly 350 processing steps are required to convert a bare silicon wafer surface to a semiconductor chip of sufficient complexity and quality to be used, for example, in high performance logic devices found in personal computers. The most common processing steps of semiconductor chip manufacture are wafer-cleaning steps, accounting for over 10% of the total processing steps. These cleaning steps are normally one of two types: oxidative and etch (or a combination of the two). During oxidative cleaning steps, oxidative compositions are used to oxidize the silicon or polysilicon surface, typically by contacting the wafer with aqueous peroxide or ozone solution. During etch cleaning steps, etching compositions are used to remove native and deposited silicon oxide films and organic contaminants from the silicon or polysilicon surface before gate oxidation or epitaxial deposition, typically by contacting the wafer with aqueous acid. See, for example, L. A. Zazzera and J. F. Moulder, J. Electrochem. Soc., 136, No. 2, 484 (1989). The ultimate performance of the resulting semiconductor chip will depend greatly on how well each cleaning step has been conducted.
In the development of cleaning semiconductor wafers, several chemistries have been explored, and a few remain as the industry standards. These industry standards are known as Standard Clean-1 (SC-1; also known as RCA-1) and Standard Clean-2 (SC-2; also known as RCA-2). SC-1 has an alkaline pH and contains ammonium hydroxide (NH4OH), hydrogen peroxide (H2O2) and water. Typically, SC-1 is used in the first step to remove metal ions and oxide surface organic materials. This procedure is then followed by application of SC-2, to remove heavy metals, alkalis and metal hydroxide contaminants. SC-2 has an acidic pH and contains hydrochloric acid, hydrogen peroxide and water. If a semiconductor wafer is heavily contaminated with organic material solutions of sulfuric acid (H2SO4) and hydrogen peroxide (H2O2) may be used. These solutions are called Piranha. (See Burkman et al., Handbook of Semiconductor Wafer Cleaning Technology, Chapter 3, Aqueous Cleaning Processes; 120-3). Other materials that have been used to clean wafer surfaces include aqueous solutions of HF, HBr, phosphoric acid, nitric acid, acetic acid, ozone, and mixtures thereof.